1. Technical Field
The present invention relates to a liquid crystal display device, and more specifically, to a source driver having a repair amplifier and a liquid crystal display device comprising the source driver.
2. Discussion of the Related Art
Liquid crystal display devices have merits such as decreased size, decreased thickness and lower power consumption over other types of display devices. They have been used for various types of electronic equipment such as notebook computers, office automation equipment and audio/video equipment. Specifically, active matrix type liquid crystal display devices, employing thin film transistors as switch elements, are suitable for displaying moving images.
FIG. 1 is a block diagram schematically illustrating a conventional liquid crystal display device. The conventional liquid crystal display device 100 comprises a source driver 110, a liquid crystal panel 160, a first fuse (F) 171 and a second fuse (F) 172.
The source driver 110 comprises digital-to-analog converters (DAC) 120, normal amplifiers 130, an output detection circuit 140 and a repair amplifier 150.
A plurality of digital-to-analog converters 120 and a plurality of normal amplifiers 130 are provided in the source driver 110. Source line driving signals, which are outputs of the normal amplifiers 130, are also output from the source driver 110. Each source line driving signal is represented by the reference numeral Yn. The source line driving signals Yn are generated by an inverted signal of a polarity control signal POL, and are inverted signals of an n-th source line driving signal Yn.
Each DAC 120 converts a digital image signal D_DAT into analog image signals, VP and VN, and outputs the converted signal. The analog image signals VP and VN indicate a gray level voltage.
Each normal amplifier 130 amplifies the analog image signals VP and VN in response to the polarity control signal POL and generates the source line driving signal Yn, which drives source line SLn of the liquid crystal panel 160. The polarity control signal POL is a signal controlling the polarity of liquid crystal and is to be inverted every frame so as to prevent deterioration of the liquid crystal panel 160. Each normal amplifier 130 can be implemented as a single amplifier or a rail-to-rail amplifier.
When an open circuit defect (indicated by the letter A in the figure) is generated in one of the source lines SLn, which can be due to errors made during the manufactur of the liquid crystal panel 160, the first and second fuses 171 and 172 can be melted with a laser to connect the metal lines arranged at both ends of the first and second fuses 171 and 172.
The output detection circuit 140 generates a detection signal DET, in response to the source line driving signal Yn, that is applied when the metal lines at both ends of the first fuse 171 are connected by a laser. For example, when the voltage level of the source line driving signal Yn ranges between VDD/2 and VDD, which is hereinafter referred to as a positive voltage, the output detection circuit 140 generates the detection signal DET of a high level. Similarly, when the voltage level of the source line driving signal Yn ranges between VSS and VDD/2, which is hereinafter referred to as a negative voltage, the output detection circuit 140 generates the detection signal DET of a low level. The output detection circuit 140 can be implemented as an operational amplifier, wherein a reference voltage applied to the inverting input terminal of the operational amplifier may be VDD/2.
The repair amplifier 150 amplifies the source line driving signal Yn transmitted through the first melted fuse 171, in response to the detection signal DET and generates a repair source line driving signal Yn—R. The repair source line driving signal Yn—R drives, through a repair line RL, a part of the source line SLn that is not driven due to an open-circuit defect A.
The liquid crystal panel 160 comprises a plurality of pixels 161. Each pixel 161 has a switch transistor TR and a liquid crystal capacitor CLC. The switch transistor TR is turned on or turned off in response to a signal driving a gate line GL. One end of the switch transistor TR is connected to source lines SLn. The liquid crystal capacitor CLC is connected between the other end of the switch transistor TR and a common voltage VCOM. The common voltage VCOM can be VDD/2.
FIG. 2 is a circuit diagram illustrating an example of the repair amplifier shown in FIG. 1. Referring to FIG. 2, the repair amplifier 150 has switch circuits (151, 153, 154 and 156) and amplifiers (152 and 155). The two amplifiers 152 and 155 constitute a single amplifier.
Each switch circuit 151, 153, 154 and 156 includes an inverter and a transmission gate. Each switch circuit 151, 153, 154 and 156 is turned on or turned off in response to the detection signal DET.
Each amplifier 152 and 155 can be implemented with an operational amplifier configured as a voltage follower. The first amplifier 152 amplifies a positive voltage of the source line driving signal Yn, transmitted when the detection signal DET has a high level, and supplies the amplified positive voltage to the repair source line driving signal Yn—R. The second amplifier 155 amplifies a negative voltage of the source line driving signal Yn, transmitted when the detection signal. DET has a low level, and supplies the amplified negative voltage to the repair source line driving signal Yn—R.
Since the conventional source driver 110 of a liquid crystal display device comprises the output detection circuit 140 implemented with an operational amplifier, which is an analog circuit, power consumption can be high due to consumption of standby current, etc. In addition, generation of the repair source line driving signal Yn—R can be delayed due to resistor-capacitor (RC) delay of the output detection circuit 140.